Microbes are found in almost every habitat present in nature.... it is very likely that even though we ingest huge ammounts of disgusting fast food this would not make your body an environment hostile enough to kill any given microbe.
the first part of that is true, microbes are found in nearly every extreme environment known to us. However, the same microbes are not found in all (and in most cases even > 1) of these environments, and a great number of them can't survive "normal" conditions. It is extremely likely (though not guaranteed) that a microbe that is suited to survive frozen for that amount of time would be killed by the temperature, PH balance, etc. of the human body
"furthers evolution" there is no furthering evolution, there are just different pressures.
Actually, the point I was going for is that it does not "work against" evolution, because evolution is merely the process of reaction to selective forces, so I'll agree with you that I may have mis-worded what I was trying to say.
Why is genetic diversity such an issue in a world where genetics can be altures invitro?
it wouldn't be, but that's not the situation. We are not altering genetics, we are selecting which embryo to implant based on the embryos' genetics. If this is done enough times, certain "unfavorable" alleles may get completely erased from our gene pool. In that case, this process is unable to bring those traits back
There isn't a lot of evolutionary need to hair or eye color anymore, if ever.
While the physical characteristics may not be necessary, sometimes genes can interact with each other in complex and unforeseeable ways. For instance, people who carry the sickle-cell gene are immune to malaria. It is not entirely unimaginable that a disease could exist that kills everyone except people with brown hair and brown eyes (perhaps a bacteria that is sensitive to high levels of melanin). If that disease strikes a population that has artificially selected against brown hair and brown eyes, the effect would be devastating
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